Tilling and other farm machinery adapted to be drawn through the soil to plow, till, inject, harrow, or otherwise treat or modify the soil is subject to hazards presented by various obstacles in the soil. Rocks, roots, hardpan, sod, and residual stubble and other plant material remaining in the soil (all of which shall be hereinafter referred to as "trash") can impede and foul such equipment and even can break it. To help minimize these problems, coulters are conventionally mounted in front of such ground-engaging equipment.
Coulters employ rotary, disc-shaped knives adapted to roll over the ground in the direction of travel of the equipment. The rotary knives are thrust into the soil for a selected distance to cut trash, ensuring a relatively clear route for the tillage equipment that follows.
For various reasons, it is desirable that the rotary knives of coulters be pressed into the ground by a spring or comparable resilient means. Preferably, when a plurality of coulters are employed on a single piece of tillage equipment that is comparatively wide each coulter is individually biased against the ground by such a spring. By this means, each coulter separately moves up and down to follow unevennesses in the ground being tilled. In addition, if the blade of a spring-biased coulter encounters an obstacle it cannot cut, it can be so adapted as to travel up and over the obstacle, thereby avoiding damage to the coulter. Some of these same considerations also apply to discs, rotary hoes, and other tilling devices in which a tillage blade rolls over and cuts or pierces into the soil.
Those skilled in the art are cognizant of a variety of spring mountings adapted to resiliently press the rotary blade of a coulter or similar implement into the ground. Examples include Lambert, U.S. Pat. No. 636,342, Taylor, U.S. Pat. No. 1,642,908, Hentrich, U.S. Pat. No. 3,700,037, Washburn, U.S. Pat. No. 3,589,449, Siekmeier, U.S. Pat. No. 3,967,685, and Whalen, U.S. Pat. No. 4,194,575. In each of these patents single coulters or similar, disc-shaped tillage tools are biased against the ground by springs arranged in a variety of ways. Comparable devices are currently being marketed, including coulters sold by Wil-rich, Inc., Wahpeton, N. Dak., and incorporated in that company's coulter chisel plow Model No. CA10CPW10 and related plows and on the Wil-rich mold board plows of which Model No. 2940-500(AR) is typical. Yetter Manufacturing Company of Colchester, Ill., sells such structures for application to chisel plows and the like as Model No. 2930 (straight shank) and 2950 (offset shank) disc-chisels. A comparable device is sold by Thurston Mfg. Co. of Thurston, Nebr. as a "Spring-cushioned Plow Coulter." A spring-loaded coulter assembly is also shown as part of pull-type liquid ammonia applicators sold as Model No. 4200 by DMI, Inc. of Goodfield, Ill. Parker, U.S. Pat. No. 1,621,739 shows a spring loading of an entire gang of discs to cause the gang to be pressed into the soil under resiliently applied pressure.
In all of the spring-biased coulter or coulter-like structures referred to above, the spring is exposed. As a consequence, the spring may become fouled with mud, trash, or other material. When this occurs, movement of the spring can be restricted or even prevented until it becomes at least no more than semi-functional. Such fouling requires that tillage be interrupted while the machinery is cleaned out. The resulting down time can be significant, especially when tillage conditions are unfavorable. The increased use of large tractors pulling wide cultivation machinery having many spring-loaded discs, coulters, or the like makes the problem even more serious. The opportunities for fouled springs are multiplied, and the cost of down time is likewise multiplied, as the entire rig is stopped even to clean isolated fouled springs.
Price, Jr., U.S. Pat. No. 2,588,872, and Whisenant, U.S. Pat. No. 2,851,939 show spring-loaded, disc-shaped tillage implements in which the spring is enclosed in a housing that thus protects it from fouling. In Whisenant the spring merely cushions the drop of a furrow wheel when a disc or plow employing the furrow wheel is lifted from the ground. In Price, however, a spring within a housing is used to bias a gang of discs against the ground. However, whereas most of the spring-urged coulters and tillage implements referred to above provide for a backward and upward movement of a pivotably mounted coulter or tillage blade as it encounters and rides up and over an obstacle, the arrangement shown in Price is limited to vertical movement of a telescoping shaft on which a gang of discs is mounted.